CODES AND STANDARDS ENHANCEMENT INITIATIVE (CASE)

Residential Refrigerant Charge Testing and Related Issues

This report was prepared by the California Statewide Utility Codes and Standards Program and funded by the California utility customers under the auspices of the California Public Utilities Commission. Copyright 2011 Pacific Gas and Electric Company, Southern California Edison, SoCalGas, SDG&E. All rights reserved, except that this document may be used, copied, and distributed without modification. Neither PG&E, SCE, SoCalGas, SDG&E, nor any of its employees makes any warranty, express of implied; or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any data, information, method, product, policy or process disclosed in this document; or represents that its use will not infringe any privately-owned rights including, but not limited to, patents, trademarks or copyrights

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 5

1.1.1

PurposeIntroduction:

The California Investor Owned Utilities (IOUs) are actively supporting the California Energy Commission (CEC) in developing the states building energy efficiency standard (Title 24) through their Codes and Standards (C&S) program. The joint intent of the IOUs and CEC is to achieve significant energy savings through the development of reasonable, responsible, and cost-effective code change proposals for the 2011 code update. Through Codes and Standards Enhancement (CASE) Studies, the IOU C&S Program provides standards and code-setting bodies with the technical and cost-effectiveness information required to make informed judgments on proposed regulations for promising energy efficiency design practices and technologies. This CASE study focuses on measuring refrigerant charge and proper operation of residential air conditioning systems. It includes a new protocol designed to work under various outdoor and indoor temperature conditions that will allow verification testing during the winter months, something that is not possible using the current method specified in RA3.2 and 3.3 of the 2008 Residential Appendices. The outcome of this study and subsequent actions by the California Energy Commission should improve compliance with air conditioner installation standards. Work on this CASE study was funded by the IOU C&S program, and work was conducted by Bruce Wilcox, P.E. and Proctor Engineering Group, Ltd.1.2 Problem Statement:

Most residential air conditioners undergo final assembly at the location of their installation, far from the production line and manufacturing quality control. As a result many of the new air conditioners in California fail to achieve their rated efficiency due to improper amounts of refrigerant, improper evacuation, metering device malfunctions, and other problems. To address this situation, the California Building Energy Efficiency Standards define methods of verifying correct charge and proper air conditioner system operation. These methods were developed from the major manufacturers specifications and verification protocols and outlined in the 2008 Title 24 part 6 (2008 Title 24 henceforth) Reference Residential Appendix RA 3.2.2. These requirements caused significant problems for HERS raters and contractors as the 2008 Title 24 Standards were implemented in early 2010. Implementing these methods on a statewide basis has revealed a number of shortcomings of these methods.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 6

There was no winter HERS verification protocol to obtain a certificate of occupancy or closing a permit1. Most manufacturers specify a single target subcooling for setting the amount of refrigerant, regardless of the test conditions. This is problematic because, with a fixed amount of refrigerant, the actual subcooling varies with differing indoor and outdoor conditions. As a result the contractor might set the refrigerant to meet the standard under one set of conditions, but the HERS rater might test and fail the unit under a different set of conditions. Air conditioners with microchannel condenser coils (which contain very little refrigerant) have been introduced into the market. These units produce even larger variations in subcooling as conditions change. The temperature split method is used as a qualifier for refrigerant charge testing. The temperature split method provides a rough indication of airflow but it is subject to both false positives (airflow OK) and false negatives (airflow not OK). It can give different answers for the same unit when nothing is changed except the operating conditions. In addition to addressing questions raised during the implementation of the 2008 Title 24 Standards, this CASE study addresses a couple of additional issues: On occasions where the installation technician fails to evacuate the system properly, there will be air (non-condensables) mixed with the refrigerant. This mix will cause mischarge of the unit and reduced efficiency. Shortcomings in the current national SEER test and rating procedure. On the positive side, the implementation of the SEER 13 National Standard has resulted in the use of thermal expansion valves (TXVs) in virtually all new residential air conditioners. This makes some simplification possible. This study also provided the opportunity for manufacturers to test their Charge Indicator Displays in a laboratory setting.

1 Local building departments could provide conditional approval. 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 7

2.

Overview

a. Measure Title b. Description

Refrigerant Charge Testing Protocols for Residential HVAC Systems This CASE topic proposes changes to the methods of verifying correct charge and proper air conditioner system operation for residential split systems for space cooling. These changes allow additional procedures to conduct testing under low outside air temperatures, they modify criteria for testing with the subcooling method, they eliminate the temperature split qualification method, and they propose a new charge method for systems with microchannel condenser coils. Prescriptive Requirement - The change would add additional methods of verifying compliance with the existing prescriptive refrigerant charge requirement. Modeling - The change would not modify the calculation procedures or assumptions used in making performance calculations. Documents The following documents are affected: 1. Residential Appendix RA3 2. Joint Appendix J6 3. Residential ACM Approval Manual 4. Residential CF-4R and CF-6R

There is no change in the energy benefits relative to the 2008 Standards aside from potential improved compliance. These changes can produce a higher level of compliance with the Refrigerant Charge Testing Requirement and lower the cost of verification. The measure has no adverse environmental impact.

Measure Availability: All materials required for the proposed changes to the reference appendices already exist. Useful Life, Persistence, and Maintenance: No change is being proposed to the useful life, persistence or maintenance of affected systems.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 8

h. Performance Verification of the Proposed Measure

The proposed methods are improvements over the existing testing protocols in the 2008 Title 24 standards. They allow refrigerant charge testing over a larger set of environmental conditions and are less likely to produce false failures.

i. This will improve cost effectiveness by eliminating the wait time between AC Cost installation and HERS verification for some units. Effectiveness j. Analysis Tools k. Relationship to Other Measures No new analysis tools are needed. The Airflow and Fan Watt Draw measure becoming mandatory simplifies the Refrigerant Charge Testing Protocol by making the temperature split method unnecessary.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 9

3.3.1

MethodologyScope of Work:

The work consisted of a series of laboratory tests on two typical split system air conditioners to test protocols and provide performance data under a range of refrigerant charge and environmental conditions. The test conditions included undercharge and overcharge, as well as outdoor temperatures from cold (37F) to hot (95F) all in the cooling mode. The work also included a review of the temperature split method. The following items were investigated under this CASE study: Testing a potential winter charge testing procedure utilizing a restriction in the outflow from the condenser fan. Adjusting the limits of acceptability for subcooling for the HVAC installer and the HERS rater based on the change in efficiency outcomes. Providing achievable methods of setting refrigerant charge on air conditioners with small refrigerant passages. Testing the efficiency effect of improper evacuation and non-condensables in the refrigerant. Improving the test method that rates the cycling efficiency of units, particularly in Californias dry climates. Testing the response of Charge Indicator Devices (CIDs) to various conditions of refrigerant charge, airflow, and climate conditions. Details of the conditions of the tests are listed in 7.1 Appendix A: Intertek Testing Conditions.3.2 Description of Laboratory Tests

3.2.1 Equipment The tested air conditioners were nominal 2.5 ton SEER 14 units with TXVs and R-410A refrigerant. The outdoor unit consisted of the condenser, compressor and condenser fan. The indoor units were common evaporator coils enclosed in ductwork and supplied with the appropriate Thermostatic Expansion Valves (TXV). This equipment is of current manufacture. The units were installed with a 50 foot lineset to simulate typical installations. 3.2.2 Test Facility These tests were performed at the Intertek psychrometric rooms in Plano, Texas. This facility is regularly used by the manufacturers to certify their units to AHRI. The facility consists of a climate controlled indoor room and a climate controlled outdoor room. The facility has the ability to cover a wide range of climate conditions from very hot summer conditions to very cold winter conditions.

Variable Speed Fan

Figure 1. 3.2.3 Performance Measures The instrumented facility provided data to produce the following common performance metrics: Sensible Capacity the amount of cooling as temperature reduction in BTU/hr. Latent Capacity the amount of cooling as dehumidification in BTU/hr. Total Capacity the total cooling including both sensible and latent capacity Sensible EER The sensible capacity divided by the watt draw Total EER The total capacity divided by the watt draw

Variable Speed Fan

Figure 1. Testing Equipment Schematic

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 12

3.3

Test Descriptions

Two types of tests were conducted - Steady State and Cycling. The Steady State tests consisted of running the air conditioner and adjusting the rooms conditions until all the parameters were maintained within the limits set for certification testing. Once steady state was achieved, the parameters were recorded for 20 minutes. The test summaries in 7.2 Appendix B: Steady State Test Summaries present the parameter averages over the 20 minute test period. The Cycling tests consisted of adjusting the rooms conditions until all the parameters were maintained within the limits set for certification testing. Once the conditions were stabilized, the parameters were continuously recorded for the duration of the tests. The cycles alternated 6 minutes of compressor running with 24 minutes of the compressor off. This test sequence is the sequence used in the SEER cycling test also known as DOE Test D2. The test summaries in 7.3 Appendix C: Cycling Test Summaries present the maximum cumulative performance over the test cycle as well as the average test rooms conditions.3.4 Temperature Split Investigation

The temperature split method is a qualitative airflow indicator that fits easily into technicians standard diagnostic tests. Temperature split is the difference between the supply plenum dry bulb temperature and the return plenum dry bulb temperature. This temperature difference is a strong indicator of the correct operation of the air conditioner. For any given set of conditions (return plenum wet and dry bulb temperature and outside coil inlet temperature), there is an expected temperature split for a proper operating unit. The expected temperature split is the Target Split. A measured temperature split within 3F of the Target Split is considered acceptable. A measured temperature split outside that range is a strong indication that there is a problem with the machine. When the temperature split is too large it is an indication of low airflow through the inside coil. When the temperature split is too low it usually indicates low cooling capacity which can be associated with a number of problems including: improper refrigerant charge, dirty outside coil, low airflow through the outside coil, compressor problems, contaminated refrigerant, restrictions in lines, orifice problems, and others. Temperature split is an imprecise tool because it is the interaction between the airflow, the cooling capacity of the unit and the indoor and outdoor conditions. The most common version of the method is used by Carrier Corporation and other manufacturers (Carrier 1994). That version only takes into account the return wet bulb and dry bulb temperature and has been found to give biased results with respect to return wet bulb temperature (Downey & Proctor 2002).

Residential Refrigerant Charge Testing and Related Issues

Page 13

The Carrier version also does not account for differences in the outdoor temperature and suggested changes have been made for improving its accuracy (Downey & Proctor 2002; Temple 2008; Mowris 2010). At this point there is no consensus on any revised version of the temperature split method. It is common for the personnel not familiar with the pitfalls of the temperature split method to misinterpret the results of the test. There have been suggestions that other methods be used whenever practical and possible ([CEC 2001]; Downey & Proctor 2002; Metoyer, Swan, & McWilliams 2009). The proposals for the 2013 Standards include making measured airflow a mandatory measure. When this is accomplished, there will no longer be a need to use the temperature split method.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 14

4.4.1

Analysis and Results

Summary Findings

The current acceptance limits for HERS verification are too narrow to avoid false failures at the time of the HERS verification test. New limits are proposed based on an acceptable range of efficiency variation. Air conditioner refrigerant charge can be successfully adjusted using a low temperature protocol. The proposed protocol achieves Sensible EERs that are within 2% of the Sensible EERs using the summer charge test protocol. Charging to a target liquid line temperature is a valid method of obtaining correct and uniform refrigerant charge levels and produces superior charging results on low volume coils. The method should be an accepted alternative. Improper evacuation leaves non-condensables mixed with the refrigerant. Even a mild amount of non-condensables produce a 7.5% reduction in Sensible EER. Commonly used certification laboratories can run valid cycling test at conditions more representative than the current SEER cycling test. When the improved test method is used it points to potential savings in hot climates of up to 41%. Charge Indicator Displays (CIDs) show promise in providing constant monitoring of air conditioners. The laboratory tests showed that two manufacturers are close to producing units that can meet the Title 24 specifications. The full texts of these conclusions are contained in Section 4.4 Conclusions of this report.4.2 CASE Recommendations

Based on the laboratory testing as well as review of manufacturers data, available field data, and existing studies, the following changes are recommended: Approve the Condenser Outlet Air Restriction Winter Testing protocol for both contractors and HERS verifiers. Widen the subcooling acceptance limit for HERS verification of TXV system subcooling to;

Greater than 2F and Within 6F of the manufacturers specified subcooling target.

Approve liquid line temperature method for units that the manufacturer specifies the liquid line temperature method for setting charge. This method is necessary for units with small refrigerant channels such as micro-channel heat exchangers. Eliminate the temperature split method if direct airflow measurement becomes mandatory. Investigate the prevalence of non-condensables and other faults in residential split air conditioners to determine the available savings. 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 15

Support revisions to the SEER rating including upgrading the cycling test to a more representative 95F outside temperature with indoor conditions of 80F with 50% relative humidity (67F wet bulb). Continue to encourage the development and manufacture of Charge Indicator Displays meeting the specifications of the 2008 Standard. Detailed revisions to the Residential Field Verification and Diagnostic Test Protocols (2008 Title 24 Standards Appendix RA3) are contained in Section 5.4.3 Detailed CASE Findings

In this section we provide an overview of the results of the laboratory tests described above as well as a discussion of how they compare with results/data from other sources. Findings are presented individually for each of the specific areas outlined in the Scope of Work section of this document. 4.3.1 Achieving Equivalent Efficiency while Charging at Low Outdoor Temperatures In order to provide a method for verifying refrigerant charge at low temperatures, it is first important to identify the goal of the verification. Given that Title 24 is an energy efficiency building standard, the appropriate goal is achieving efficiency. This study investigated a possible low outdoor temperature refrigerant charge protocol. Virtually all the air conditioners sold in California today have Thermostatic Expansion Valves (TXVs). A TXV is a constant superheat valve that adjusts its resistance to refrigerant flow to obtain a constant superheat. The basic problem with low temperature refrigerant charging of TXV air conditioners using current procedures in the 2008 Title 24 is that the valve adjusts to its fully open position. The fully open position occurs when the pressure across the TXV is insufficient to push the required volume of refrigerant through the valve to maintain a stable superheat. This problem exists at low outdoor temperatures when the condenser saturation temperature and pressure are low. By increasing the condenser saturation temperature and pressure, the TXV can function within its design parameters and provide proper refrigerant control. In commercial building air conditioners this is accomplished by slowing down the condenser fan speed (or reducing the number of operating condenser fans). Various test methods have been attempted to increase condenser pressures and temperatures in cold weather. The two prominent methods are: 1) a tent covering the condenser unit causing recirculation of expelled warm air through the condenser and 2) blocking part of the condenser coil entrance. These two methods have generally proven unsatisfactory. The first causes major alterations in the temperatures entering the coil and the latter produces irregular flow or heat transfer through the refrigerant circuits. Lennox Corporation currently allows blocking part of the condenser coil entrance to charge some of their TXV models in the winter. The Condenser Air Exit Restriction (CAER) Protocol overcomes these issues. Restricting the outlet from the condenser fan without disturbing the inlet conditions has proven to be a viable method of low temperature testing. Bringing the pressure drop across the TXV to at least 160 psi for R-410A has the same effect as higher test temperatures. An example of a CAER is shown in Figure 2. 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 16

Figure 2. An Example of a Condenser Air Exit Restrictor The sequence of each proof test at Intertek consisted of: Baselining the efficiency of two air conditioners at standard conditions with refrigerant adjusted to the manufacturers specification. Undercharging and Overcharging the units to obtain a 5% loss in Sensible Efficiency Lowering the indoor temperature and outdoor temperature to provide severe winter conditions. Restricting the outflow from the condenser fan without disturbing the inlet to the coil. Recharging (adding or removing refrigerant) to produce the manufacturers specification with the unit in the cold/restricted condition. Bringing the units back to standard conditions and determining the sensible efficiency of the units charged using the CAER protocol. Rerunning the unit with baseline charge adjustment for final comparison. The results of the testing as illustrated in Figure 3 and Figure 4 below and detailed in 7.2 Appendix B: Steady State Test Summaries are used to produce a protocol that limits the sensible efficiency effect of refrigerant charge to substantially less than 5%.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 17

Figure 3: Energy Efficiency Ratio Comparison: Standard and Low Temperature Methods The efficiency of both units adjusted using the Condenser Air Restriction Protocol (Cold Weather Recharge) was less than 2% different from the average baseline efficiency of those units adjusted with the standard (summer) protocol.

Residential Refrigerant Charge Testing and Related Issues

Page 19

4.3.2 Subcooling Acceptance Limits Subcooling in this section is always in degrees Fahrenheit. The variability of subcooling with outdoor and indoor conditions has been ignored for many years. It has always been present, but the results have generally been considered good enough for field adjustment of refrigerant levels. The advent of air conditioners with less refrigerant volume and the need for charging and verification over a range of conditions necessitates taking these variations into account. This study investigated the possible acceptance limits for subcooling based on the effect the limits would have on the efficiency of the air conditioner. Subcooling Variability with Identical Refrigerant Charge Figure 5, courtesy of Trane Corporation, shows the subcooling variation for units charged at 95F (the upper line of data points) when tested at 82F (the lower cloud of data points). This variation is partially due to the difference in outdoor temperature and partially due to the differences in indoor conditions and coils (which results in different suction/low side pressures).

Figure 5: Subcooling Variation with Constant Refrigerant Charge for Microchannel Condenser Air Conditioner The tests conducted in support of the CASE study also showed variation in subcooling with outdoor temperature. The CASE study tests included two paired comparisons with identical conditions (refrigerant volume, airflow and indoor conditions) where only the outdoor temperature changed. Figure 6 shows three degrees subcooling variation with constant refrigerant charge when the outdoor temperature changes from 82F to 95F.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 20

Figure 6: Subcooling Variation with Constant Refrigerant Charge for CASE Study Air Conditioner Tests Trane ran 1800+ combinations through their simulation model for their conventional XR family of models. The resulting variation from outdoor temperature alone was similar to the lab tests in Figure 3. The plot of these model runs is reproduced in Figure 7.

Residential Refrigerant Charge Testing and Related Issues

Page 21

When variations with test conditions are combined with achievable limits of measurement variation, it is clear that the existing standard protocol will, at times, produce a pass for the contractor and a fail for the HERS verifier. This situation produces the question of the sensitivity of efficiency to variations in subcooling and refrigerant charge. The laboratory tests were designed to determine the range of subcooling that would achieve 5% or less variation in efficiency. Relative Independence of Efficiency from Refrigerant Charge and Subcooling Differences The efficiency of a TXV unit is nearly constant over a wide range of refrigerant charge and measured subcooling. This is illustrated by laboratory and field tests including the items below. Figure 7 shows the small variation in efficiency as refrigerant charge is modulated from 20% undercharged to 20% overcharged for TXV systems (dashed lines). Graph courtesy PG&E Technical and Ecological Services (Report 491-01.4). EER is normalized to the total EER at 95F outside.

Figure 8: Normalized EER versus Charge and Outside Temperature

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 22

Figure 9: Normalized EER versus Charge in CASE Study at 95F Outside Figure 9 shows the same typical efficiency response from the two units tested as part of this CASE study. Sensible EER is normalized to the Sensible EER at full charge (Manufacturers specified subcooling of 7F)

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 23

The important metric in determining the allowable range of subcooling is how much the Sensible EER changes with refrigerant charge and the indicative subcooling changes. Figure 9 reconfigures the normalized EER curve in Figure 8 to show its relationship to subcooling. Figure 10 shows the range of subcooling at 95F in the CASE study as well as the recommended acceptable limits on subcooling by HERS raters.

Recommended Range of Acceptance Manufacturers Spec. Subcooling

Figure 10: Normalized EER versus Subcooling in CASE Study Based on the above tests and earlier laboratory testing, an acceptable verification range is proposed. On the low end, a minimum subcooling greater than 2F and no less than target -6F achieves the goal of limiting efficiency variations due to undercharge. At the same time it does not exclude units for which manufacturers specify a subcooling of 3F. On the high end, a maximum subcooling of target + 6F over-achieves the goal of limiting efficiency variations due to overcharge. In all cases the installing technician is still held to the original range of acceptability set by the existing standard and is responsible for charging to the manufacturers specifications. As illustrated in Figure 10 the recommended range of acceptance limits the sensible efficiency effect to substantially less than 5%.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 24

4.3.3 Liquid Line Temperature Charging Partially as a result of the Federal Air Conditioner Standard improvement from SEER 10 to SEER 13, the manufacturers have begun to use refrigerant heat exchangers that have a smaller refrigerant volume. This increases the variation in subcooling with changes in outdoor temperature as well as changes in indoor coil design and airflow. As an example, a microchannel unit was tested and modeled by Trane Company and produced the variations in subcooling shown in Figure 11 (Figure 5 repeated).

Figure 11: Subcooling at 82F and 95F with Constant Refrigerant Charge and Various Matched Indoor Units The unit depicted is the Trane 4TTM3036A1 with a variety of listed matching indoor units. The graph is from the Trane presentation: Development of a Charging Method for the 4TTM Family. The manufacturer found this level of variation unacceptable and has implemented a Liquid Line Temperature Charging method that takes into account both the outside temperature and the indoor unit performance. An example target liquid line temperature table is shown in Figure 12. The liquid line target is determined by the outside temperature and the suction (low side) pressure. The liquid line targets are specific to each model air conditioner.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 25

Figure 12. Example of a Liquid Line Charging Table The CASE team has reviewed data from Trane for unit 4TTM3036A1 and concludes that the indication of desired refrigerant charge is more stable with changing test conditions using the manufacturers liquid line method rather than the subcooling method. In the absence of a superior method for charging units that the manufacturer specifies the Liquid Line Charging Method, the CASE team recommends that the Liquid Line Charging Method detailed in 5.3.1 be approved for use by installation technicians and HERS verifiers. 4.3.4 The Effect of Non-condensables on Air Conditioner Efficiency One persistent problem observed by field inspectors is the prevalence of improper evacuation during AC installation or repairs. The current state of affairs is that many installation technicians do not evacuate air and moisture from the refrigerant lines and inside coil prior to opening the valves releasing the stored refrigerant. This process results in misdiagnosis of refrigerant charge (the pressures are elevated above what they would be with pure refrigerant) as well as reduced AC efficiency This study measured the effect of two evacuation scenarios on air conditioner efficiency. The first scenario is believed to be the most common. In the first scenario nitrogen was introduced into the inside coil and lineset. The service valves remained open to achieve pressure balance with the atmosphere. This simulates to condition wherein the technician makes no attempt or only a marginal attempt to evacuate the system. The second scenario pressurized the inside coil and lineset with 20 psig of nitrogen. This scenario simulates a situation where the technician uses nitrogen for pressure testing, but fails to fully remove it prior to releasing the refrigerant into the system.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 26

Figure 13: Efficiency Degradation from Non-Condensables in System The results of the scenario 1 tests as shown in Figure 13 shows failure to evacuate the inside coil and lineset produces a 7.5% reduction in Sensible EER (difference between the green bar and first red bar in Figure 13). This occurred with the manufacturers nominal (shipped in the unit) refrigerant charge and produced the manufacturers specified subcooling without any addition or removal of refrigerant (in spite of a 50 foot lineset). For scenario 2, failure to fully evacuate the nitrogen used for leak testing, required only 4 lbs. and 1 ounce of refrigerant to achieve the manufacturers specified 7F subcooling (based on the high side pressure and the assumption of pure refrigerant). This weight of refrigerant is less than half the amount needed to obtain the manufacturers specified subcooling with this indoor coil and a 50 foot lineset. The hidden lack of refrigerant accounts for the 42% reduction in Sensible EER (difference between the blue bar and second red bar in Figure 13). 4.3.5 Improved Air Conditioner Cycling Test Procedure Accounting for Climate Differences California utilities are summer peaking with air conditioning causing the increased electric loads at peak demand periods. Peak electric demand dominates the need for additional power plants, transmission infrastructure and causes a variety of environmental problems. Even high-performance air conditioning systems are not optimized to reduce peak electric demand and energy under dry ambient conditions. Previous research has shown that the cycling test used for establishing SEER is not representative of installed conditions and produces results that are less than optimum for both dry climates and wet climates. In 2008 a coalition of energy advocates and experts had begun an open process to update the Federal Standards. That group had almost universally agreed that there were two fatal flaws in the 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 27

current air conditioner test procedure. 1) The fan energy consumption and test conditions were totally unrealistic; resulting in inflated ratings. 2) The test did not distinguish between air conditioners that provided good dehumidification for wet climates and superior cooling for hot dry climates. (Buntine, Proctor, and Knight 2008; Energy Solutions 2008; Henderson, Shirey and Raustad 2006; NRDC, NCLC and Enterprise Community Partners 2008; NRDC 2008; Parker et al. 1997; Proctor and Parker 1997; Proctor and Pira 2005; Proctor Engineering Group 2008; Proctor et al. 2008; Sachs 2008) Previous research including field tests, laboratory tests, and modeling have shown that much of the latent capacity (moisture removal) from air conditioners is actually in storage on the inside coil when the compressor cycle ends. This research has shown that continuing to run the air circulation fan after the compressor stops evaporates the moisture on the coil and delivers it to the building as sensible cooling and rehumidification. The prior research proved the potential of recovering the stored latent capacity as sensible capacity at low energy cost. There remained a number of questions that these tests and analyses were designed to determine: Can certification laboratories provide accurate data for cycle testing at realistic indoor conditions such that the SEER tests could be modified? What relationships exist between the rate of airflow, the available stored latent capacity, and latent recovery? What are the limitations of latent recovery within the confines of normal duct systems in hot dry climates? The purpose of this section of the CASE project is to determine how to provide high net sensible EER (defined as sensible capacity with fan heat divided by power with fan watt draw) at high outdoor temperatures, normal dry climate indoor conditions, and typical installation (typical duct system restriction). Test Description There were three series of tests covering variations in the evaporator airflow. Each series followed the standard SEER cycling test sequence: compressor on 6 minutes, compressor off 24 minutes, compressor on 6 minutes, compressor off 24 minutes, etc. repeating for five cycles. The five cycles had increasingly longer fan delays as shown in Figure 14. Figure 15 illustrates the fan delay with the fan running after the compressor powers down. Cycle Time First 0 sec Second 105 sec Third 200 sec Fourth 300 sec Fifth 610 sec

Figure 14: Fan Delay Setting for Testing

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 28

Outdoor W

PSC Fan Watts

2000

1500

1000

Fan Delay500

0 0 200 Elapsed Seconds 400 600

Figure 15: Fan Time Delay Illustration The airflow through the indoor coil was varied between the test series as shown in Figure 16. Test Series Coil Flow Compressor on Coil Flow Fan Only (Fan Delay) 0 450 450 A 350 350 B 350 216

Figure 16: Indoor Coil Airflow Settings for Tests (CFM per Ton) Finally, the outdoor and indoor conditions were different from the standard SEER cycling test in order to produce more realistic answers. The outdoor temperature was set at 95F (SEER is at 82F). The indoor conditions were held at 80F dry bulb, 67F wet bulb (50% Rh). These conditions produce a wet coil as is common in normal operation even in dry climates. The standard SEER test is run with a totally dry indoor coil, which is artificially accomplished by indoor conditions of 80F dry bulb, 57F wet bulb.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 29

Calculation The metric of interest in this research is the performance of the air conditioners at conditions as seen in most of California, Nevada, Arizona, and West Texas. These areas have low outdoor humidity under summer conditions. In these areas the introduction of outdoor air into the building dries the indoor air below 65 grains of moisture (dew point 55 F, 0.0093 lb. of water per lb. dry air). The metric is the Sensible EER. The Sensible EER is calculated in this manner: Sensible EER = Net Sensible Capacity / Total Watt Draw Net Sensible Capacity = Gross Sensible Capacity Fan Heat Gross Sensible Capacity = Air Heat Capacity x (Tevapin Tevapout) Where: Air Heat Capacity = CFM x density x specific heat capacity (using appropriate values and conversions) Tevapin = Temperature entering the evaporator Tevapout = Temperature leaving the evaporator Fan Heat = Evap. Fan Watts x 3.412 Total Watt Draw = Compressor Watts + Cond. Fan Watts + Evap. Fan Watts The following are measured with the laboratory instrumentation: Compressor Watts, Cond. Fan Watts, Tevapin, Tevapout, and CFM. The air density and air specific heat capacity are calculated based on measured parameters in the test rooms. The test procedure does not include a standard indoor fan, so simulated values are taken for the Evaporator Fan Watts. The following equations were used to simulate the Evap. Fan Watts: For a Permanent Split Capacitor Motor Fan Evap. Fan Watts = 0.51 x CFM For a Brushless Permanent Magnet Motor Fan Evap. Fan Watts = 0.000000380682 x CFM^3 - 0.000115317571 x CFM^2 + 0.063091358424* CFM Cycle Cumulative Sensible EER The testing produced instantaneous Net Sensible Capacities and instantaneous Total Watt Draw. When these instantaneous figures are summed over the whole cycle the result is the Cycle Cumulative Sensible EER. The calculation of Cycle Cumulative Sensible EER is:

CyCumSenEERi =

Where i = seconds from the start of the cycle. 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 30

The results for a single cycle from i=0 to i = 660 are shown in Figure 17.8

Sensible EER PSC at unit

0 0 200 400 Elapsed Seconds 600 800

Figure 17: Cumulative Sensible EER vs. Time Certification Laboratories and Alternative SEER Cycling Tests The testing at the Intertek laboratory showed that running SEER cycling tests with a wet coil is within their capabilities. Relationships between Airflow and Latent Recovery Effect of Airflow on Sensible EER The first indication of the relationship between airflow and stored latent capacity is the sensible EER of the unit at different airflows. Generally latent capacity is reduced and sensible capacity is increased at higher airflows. These tests confirmed what prior tests have shown. Higher airflow produced higher sensible capacity. The downside of higher airflows has always been the increase in fan watt draw necessary to obtain the higher airflows. These tests showed that, within the tested range of airflow, the Sensible EER increased in spite of the higher fan watt draws. Figure 18 shows the increased Sensible EER due to airflow in two identical tests with a 100 second fan delay.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 31

Maximum Sen. EER 8.07 450 CFM per ton

Maximum Sen. EER 6.02

350 CFM per ton

2

100

200 300 Elapsed Seconds

400

500

Figure 18: Airflow Effect on Sensible EER (PSC Fan Motor) In Figure 18 the Sensible EER for the 450 CFM scenario is higher during the compressor part of the cycle. The higher efficiency is due to a larger sensible capacity. When the higher airflows are accomplished, there is less moisture on the coil at the end of the cycle (less latent storage) and the length of the fan delay is limited by the amount of moisture on the coil. When the performance of the unit is limited by the combination of the duct system and the equipment to 350 CFM per ton (as is most common in field studies) there is more moisture on the coil and the fan delay can be lengthened to achieve higher Sensible EER. Moisture on the Coil at Start The length of the previous cycle, the length of the previous fan delay, and the airflow rate all effect the amount of moisture on the coil at the start of the cycle. In all cases with 450 CFM per ton the coil was nearly dry at the beginning of the cycle. This results in a negative Sensible EER during the startup period. This is shown as the characteristic dip below 0 Sensible EER in Figure 18. Low Fan Speed during the Fan Delay It has been proposed that lowering the fan speed during the fan delay combined with a Brushless Permanent Magnet (BPM) motor would produce even higher Sensible EERs due to the low watt draw of the BPM. This hypothesis was investigated with multiple tests. Figure 19 compares two otherwise identical tests; one with the fan speed at 350 CFM per ton and one with 216 CFM per ton during the fan delay.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 32

10

350 CFM per ton

Maximum Sen. EER 9.89 Maximum Sen. EER 9.59

350 CFM per ton

6

216 CFM per ton

0 200 400 600 Elapsed S econds 800 1000

Figure 19: Fan Delay Airflow Effect on Sensible EER (BPM Fan Motor) Effect of Duct System Efficiency on Sensible EER Delivery For the BPM motor the lab tests indicate that a long fan delay and lower airflow would be advantageous to produce higher Sensible EERs3 at the unit. This appearance may be correct for units that have no duct system or have very high distribution efficiencies. However, real ducted systems have conduction and leakage losses. These losses are important to take into account in determining the airflow range and fan delay length. The laboratory test results were analyzed for connection to a duct system that had a 20% capacity loss at full capacity. This was modeled as: Capacity Loss = C x (120F Tsupply) while the fan is operating. Where C is a constant. Duct losses modify the Sensible EER results substantially. Figure 20 shows the results for a PSC motor and 350 CFM per ton with and without duct losses.

Residential Refrigerant Charge Testing and Related Issues

Page 33

Duct loss effect with a PSC fan motor Without duct losses the peak Sensible EER in Figure 20 occurs with the longest fan time delay (610 seconds). The Sensible EER peak occurs at the end of the time delay with a value of 7.30 BTU/watt hr. With duct losses the peak occurs with the shorter time delay at 3.89 BTU/watt hr.Sensible EER PSC at unit 10 Sensible EER with PSC

200

400 600 Elapsed Seconds

800

1000

Figure 20: Duct Loss Effect on Sensible EER (350 CFM, PSC Fan Motor) Duct loss effect with a BPM fan motor The duct losses have a similar effect on the units Sensible EER when it is fitted with a BPM motor. These results are shown in Figure 21. Without duct losses the peak Sensible EER (9.89 BTU/watt hr.) occurs with the longest fan delay. With duct losses the peak Sensible EER (5.23 BTU/watt hr.) in Figure 21 occurs at a 525 second time delay.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 34

Sensible EER BPM at unit 10

Sensible EER with BPM

200

400 600 Elapsed Seconds

800

1000

Figure 21: Duct Loss Effect on Sensible EER (350 CFM, BPM Fan Motor) Duct loss effect with a BPM fan motor at 450 CFM per ton When the system can attain a 450 CFM per ton airflow, the duct loss effect does not significantly affect the optimum fan delay; however it has an obviously detrimental effect on the Sensible EER delivered. The peak Sensible EER is 8.92 without duct losses and 6.58 with the assumed duct losses.Sensible EER BPM at unit 10 8 6 Sensible EER with BPM

7.63 195 4.71 195

8.47 115 6.12 85

6.90 190 3.62 190

8.85 300 5.21 300

8.20 120 5.85 90

7.84 315 3.94 315

9.89 610 5.23 525

8.10 115 5.74 85

9.59 610 4.24 590

Figure 24: Sensible EER Summary for BPM Unit

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 37

4.3.6 Laboratory Tests of Charge Indicator Display Title 24 provides the Charge Indicator Display (CID) as an alternative to refrigerant charge checking. The benefit of the CID is that it continuously monitors the air conditioner and informs the occupant when there are specific problems with the unit. The Indicator Display takes a motion picture of AC performance, while refrigerant charge checking is a snap shot. Potential manufacturers were given the opportunity to test prototype CIDs during the test sequence. Two Charge Indicator Displays were installed in the Intertek laboratory for this study. Both units correctly identified undercharge in the early testing. The statuses of the CIDs in the summary sheets for September 20 through September 23 were not recorded. During that time there was one test that should produce a fault indication. Beginning September 28 a new unit was tested and the CIDs monitored. One of the two units properly indicated an undercharge fault when it occurred. On September 30 a fault indication was not recorded for either CID at a test condition with significant undercharge. The identical test was repeated on October 2 and one of the two units properly indicated the overcharge situation. There were no false indications of charge or airflow problems with either device. Both potential manufacturers appreciated the opportunity to test their devices and are continuing development and manufacturing plans.4.4 Conclusions

4.4.1 Acceptance Limits for HERS Verification The current acceptance limits for HERS verification are too narrow to avoid false failures at the time of the HERS verification test. The acceptance limits should be widened to account for differences in test conditions. The new limits should be based on the potential sensible efficiency effect of the limits. 4.4.2 Test Protocol for Winter Testing of Air Conditioners On TXV air conditioners refrigerant charge can be successfully adjusted using a low temperature protocol that restricts the outflow from the condenser to achieve appropriate pressure drops across the TXV. The proposed protocol achieves Sensible EERs that are within 2% of the Sensible EERs using the common summer charge test protocol. 4.4.3 Liquid Line Temperature Charging Charging to a target liquid line temperature is a valid method of obtaining uniform refrigerant charge levels at differing outdoor temperatures and differing indoor conditions. Charging to a target liquid line temperature based on the condenser air entering temperature and suction pressure produces superior charging results on low volume coils and should be accepted as an alternative method where the manufacturer specifies that method. 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 38

4.4.4 Non-Condensables and Improper Evacuation Improper evacuation leaves non-condensables mixed with the refrigerant. This condition produces erroneous determination of saturation temperatures and significantly reduced Sensible EER. Even a mild amount of non-condensables produce a 7.5% reduction in Sensible EER. 4.4.5 Improved Air Conditioner Cycling Test Procedure Accounting for Climate Differences Testing at Intertek showed that commonly used certification laboratories can run valid cycling test at conditions more representative than the current SEER cycling test. The revised test can produce metrics of significant meaning and usefulness for both dry climates and moist climates by differentiating between high Sensible EER and high Latent or Total EER. When the improved cycling test procedure is used the following practical implications are made apparent: For ducted systems installed outside the conditioned space with near 6 minute compressor cycles and airflow near 350 CFM per ton, the optimum time delay is approximately 300 seconds (five minutes) for a PSC fan motor machine. For similar conditions to a) above, the optimum time delay for a BPM fan motor machine is approximately 525 seconds (near nine minutes). For units capable of high airflows near 450 CFM per ton, the optimum fan delay is near 90 seconds regardless of the fan motor if the duct losses are 20% or less. For non-ducted units, or units with near zero duct losses and common 350 CFM per ton, the optimum fan delay for either type of fan motor is approximately ten minutes. At common conditions of 350 CFM per ton and 20% duct losses, the addition of a 5 minute fan delay increases a PSC unit Sensible EER from 2.45 to 3.89, a potential savings of 37%. At common conditions of 350 CFM per ton and 20% duct losses, the addition of a 10 minute fan delay increases a BPM Sensible EER from 3.07 to 5.23, a potential savings of 41%. 4.4.6 Charge Indicator Displays Charge indicator Displays (CIDs) show promise in providing constant monitoring of air conditioners. The laboratory tests showed that two manufacturers are close to producing units that can meet the Title 24 specifications.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 39

5.

Recommended Language for the Reference Appendices

5.1.1 RA3.2.1 Purpose and Scope

The purpose of this procedure is to determine and verify that residential split system space cooling systems and heat pumps have the required refrigerant charge and that the metering device is working as designed. The procedures only apply to ducted split system central air conditioners and ducted split system central heat pumps. The procedures do not apply to packaged systems. For dwelling units with multiple split systems or heat pumps, the procedure shall be applied to each system separately. The procedures detailed in Section RA3.2 are to be used after the HVAC installer has installed and charged the air conditioner or heat pump system in accordance with the manufacturer's instructions and specifications. Failure to follow the manufacturers instructions may result in significant refrigeration system faults that may invalidate refrigerant charge and metering device results. The installer shall certify to the builder, building official and HERS rater that he/she has followed the manufacturers instructions and specifications prior to proceeding with the procedures in this appendix. Appendix RA3.2 defines three procedures, the Standard Charge Measurement Procedure and the Liquid Line Temperature Charging Method in Section RA3.2.2, the Alternate Charge Measurement Procedure in Section RA3.2.3, The standard procedure or liquid line temperature procedure shall always be used for HERS rater verification. HVAC installers may use the alternate procedure when the outdoor temperature is below 70F. Refrigerant charging procedures other than that described in RA3.2 are possible, and when vapor compression air conditioner and heat pump system refrigerant charge and metering device operating performance can be reliably determined by methods and instrumentation other than those specifically defined in section RA3.2, such alternative charging procedures shall be allowed if the air conditioner equipment manufacturer requests approval from the Executive Director. The Executive Director will grant such approval after reviewing submittals from the applicant. Charging procedures that are approved by the Executive Director will be published as an addendum to this appendix. The applicant shall provide information that specifies the required instrumentation, the instrumentation accuracy, the parameters measured, the required calculations, the allowable deviations from target values for system operating parameters, and the requirements for system fault indication. Manufacturers shall certify to the Energy Commission that the charging procedure produces a sensible EER at 95/80/67 that is within 5% of the sensible EER produced in a laboratory test at 95/80/67 of the air conditioner with the designated refrigerant weight. Manufacturers using alternative charging procedures shall, upon request, provide comprehensive engineering specification documentation, installation and technical field service documentation, and user instructions documentation to installers and service personnel that utilize the procedure.

The following sections document the instrumentation needed, the required instrumentation calibration, the measurement procedure, and the calculations required for each procedure. The reference method algorithms adjust (improve) the efficiency of split system air conditioners and heat pumps when they are diagnostically tested to have the correct refrigerant charge and the metering device is

2013 California Building Energy Efficiency Standards

Residential Refrigerant Charge Testing and Related Issues

Note that diagnostically testing the refrigerant charge requires a minimum level of airflow across the evaporator coil, as specified in the Section 150 of the Standards.

5.1.2 RA3.2.2 Standard Charge Measurement Procedure

This section specifies the Standard charge measurement procedure. Under this procedure, required refrigerant charge is calculated using: 1. The Superheat Charging Method for Fixed Metering Devices or 2. The Subcooling Charging Method for Thermostatic Expansion Valves (TXV) and Electronic Expansion Valves (EXV), or 3. The Liquid Line Temperature Charging Method, or 4. An Alternative Charging Method specified by the Manufacturer and approved by the Executive Director. The standard procedures detailed in this section shall be completed within the manufacturers specified temperature range after the HVAC installer has installed and charged the system in accordance with the manufacturers specifications. All HERS rater verifications are required to use a standard procedure. This procedure does not relieve the installing contractor from any obligations to follow manufacturers specifications. This procedure is used to assure conformance to Title 24.

..... NOTE: All intervening sections remain as is. 5.1.3 RA3.2.2.2 Instrumentation SpecificationsInstrumentation for the procedures described in this section shall conform to the following specifications: RA3.2.2.2.1 Digital Thermometer Digital thermometer shall have dual channel capability in Celsius or Fahrenheit readout with: 1. Accuracy: 1.8F, 2. Resolution: 0.2 F. RA3.2.2.2.2 Temperature Sensors and Temperature Measurement Access Holes (TMAH) Measurements require three (3) temperature sensors that pass the following test: A test point at dry bulb temperature T1 The temperature sensor stabilized at T2 The absolute value of (T1 minus T2 ) is greater than 40F When the sensor is moved to the test point, the sensor has a response time that produces the accuracy specified in Section RA3.2.2.2.1 within 90 seconds of insertion. Measurements require one (1) cotton wick for measuring wet-bulb temperatures or an electronic gauge that is calibrated to be within the tolerances in RA3.2.2.2.1 Measurements require two (2) pipe temperature sensors that pass the following test: 1. 2. 3. 4.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 41

1. Six pipes (1/4 dia., 3/16 dia., 3/8 dia., 3/4 dia., 7/8 dia., 1 1/8 dia.) at temperature T1 in an environment at T2 where the absolute value of (T1 minus T2 ) is greater than 40F 2. The temperature sensor is stabilized at T 2 3. The sensor has a response time that produces the accuracy specified in Section RA3.2.2.2.1 within 90 seconds of application to the pipe of the size for which it is approved. A sensor may be used for more than one pipe size if it passes the above test for each pipe size for which it is used. There shall be one labeled temperature measurement access hole in the supply plenum. The temperature measurements shall be taken at the following location:

The location shall have a 5/16" (8 mm) diameter hole. The location shall be labeled "Title 24 Return Temperature Access" in at least 12-point type. This location can be in any one of the four sides of the plenum. RA3.2.2.3 Digital Refrigerant Gauges A digital refrigerant gauge with an accuracy of 3 psig discharge pressure and 1.0 psig suction pressure shall be used. Other saturation temperature measurement sensor instrumentation methodologies shall be allowed if the specifications for the methodologies are approved by the Executive Director.

...

5.1.4 RA3.2.2.5 Set up for Charge Measurement

Except for winter charging using the Standard method, the unit should be set up as it normally operates.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 42

For winter charging using the Standard method, the unit should be set up as described in this section if the manufacturer has approved the use of this winter charging method: 1. Install the condenser outlet air restrictor on the outlet from the condenser fan: a. Position the restrictor so it does not interfere with the inlet airflow to the condenser. b. Start the air conditioner or heat pump in the cooling mode and restrict the outlet until the difference between the high side pressure and the low side pressure is between 160 psi and 220 psi for R-410A refrigerant and 100 to 145 psi for R-22 refrigerant. 160 psi (Phigh, Plow ) 220 psi for R-410A refrigerant; 100 psi (Phigh, Plow ) 145 psi for R-22 refrigerant c. Allow the unit to stabilize for 15 minutes, make sure the pressure is still 160 psi (Phigh, Plow ) 220 psi for R-410A refrigerant 100 psi (Phigh, Plow ) 145 psi for R-22 refrigerant 2. Note 1: Refer to Energy Commissions website for the list of split system air condition units approved by the manufacturers to use the Winter Charge Setup. In addition to the requirements of this document, manufacturers may issue additional instructions/clarification for the equipment and procedures to be used to conduct the Winter Charge Setup. These additional instruction/clarifications are also available on the Energy Commission website. http://www.energy.ca.gov/title24/ Note 2: Winter Charge Setup may be used for manufacturer approved systems that use a target subcooling for refrigerant charge, including units equipped with micro-channel heat exchangers where the manufacturer specifies subcooling for measuring refrigerant charge. Note 3: Similar to the Standard Charge Measurement Procedure for warm weather, the Winter Charge Setup may be used by the Installer and/or the HERS Rater.

5.1.5 RA3.2.2.5 Charge Measurement

The following procedure shall be used to obtain measurements necessary to adjust required refrigerant charge as described in the following sections: 1. If the condenser air entering temperature is less than 65F, establish a return air dry bulb temperature sufficiently high at the beginning of the test that the return air dry bulb temperature will be not less than 70F at the end of the 15-minute period in step 2. 2. Connect the refrigerant gauges to the service ports, taking normal precautions to not introduce air into the system. 3. Turn the cooling system on and let it run for 15 minutes to stabilize temperatures and pressures before taking any measurements. While the system is stabilizing, proceed with setting up the temperature sensors. 4. Attach one pipe temperature sensor to the suction line near the suction line service valve, with the sensor on the top of the pipe between 10 oclock and 2 oclock, and attach one pipe temperature sensor to the liquid line near the liquid line service valve. 5. Attach a temperature sensor to measure the condenser entering air dry-bulb temperature. The sensor shall be placed so that it records the average condenser air entering temperature and is shaded from direct sun. 6. Ensure that all cabinet panels that affect airflow are in place before making measurements. The temperature sensors shall remain attached to the system until the final charge is determined. 7. If a fixed metering device using a cotton wick sensor, place wet-bulb temperature sensor (cotton wick) in water to ensure it is saturated when needed. Do not get the dry-bulb temperature sensors wet.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 43

8. At 12 minutes, insert a dry-bulb temperature sensor (and a wet-bulb temperature sensor if a fixed metering device) into the return plenum at the "Title 24 Return Temperature Access" detailed in Section RA3.2.2.2.2. 9. At 15 minutes when the return plenum wet-bulb temperature reading has stabilized (if present), using the temperature sensors already in place, measure and record the return (evaporator entering) air dry-bulb temperature (Treturn, db) and the return (evaporator entering) air wet-bulb temperature (Treturn, wb) (if present). 10. Using the refrigerant gauge or saturation temperature measurement sensor already attached, measure and record the evaporator saturation temperature (T evaporator, sat) from the low side gauge. 11. Using the refrigerant gauge or saturation temperature measurement sensor already attached, measure and record the condenser saturation temperature (T eondenser, sat) from the high side gauge. 12. Using the pipe temperature sensor already in place, measure and record the suction line temperature (Tsuction,). 13. Using the pipe temperature sensor already in place, measure and record the liquid line temperature (T liquid). 14. Using the dry-bulb temperature sensor already in place, measure and record the condenser (entering) air dry-bulb temperature (Tcondenser, db). The above measurements shall be used to adjust refrigerant charge as described in following sections.

5.1.6 RA3.2.2.6 Refrigerant Charge and Metering Device Calculations

The following steps describe the calculations to determine if the system meets the required refrigerant charge and metering device function using the measurements described in Section RA3.2.2.5. If a system fails, then remedial actions must be taken. Be sure to run the air conditioner for 15 minutes after the final adjustments before taking any measurements. RA3.2.2.6.1 Fixed Metering Device Calculations The Superheat Charging Method is used only for systems equipped with fixed metering devices. These include capillary tubes and piston-type metering devices. 1. Calculate Actual Superheat as the suction line temperature minus the evaporator saturation temperature. Actual Superheat = Tsuction, Tevaporator, sat. 2. Determine the Target Superheat using Table RA3.2-2 using the return air wet-bulb temperature (Treturn, wb) and condenser air dry-bulb temperature (Tcondenser, db). 3. If a dash mark is read from Table RA3.2-2, the target superheat is less than 5F. Note that a valid refrigerant charge verification test cannot be performed under these conditions . A severely undercharged unit will show over 9F of superheat. However overcharged units cannot be detected from the superheat method. The usual reason for a target superheat determination of less than 5F is that outdoor conditions are too hot and the indoor conditions are too cool. One of the following is needed so a target superheat value can be obtained from Table RA3.2-2 either 1) turn on the space heating system and/or open the windows to warm up indoor temperature; or 2) retest at another time when conditions are different. Repeat the measurement procedure as necessary to establish the target superheat. Allow system to stabilize for 15 minutes before the final measurements are taken. 4. Calculate the difference between actual superheat and target superheat (Actual Superheat - Target Superheat). 5. In order to allow for inevitable differences in measurements, the Pass/Fail criteria are different for the Installer and the HERS Rater. For the Installer, if the difference is between minus 5F and plus 5F, then the system passes the required refrigerant charge criterion. For the HERS Rater inspecting the system, if the difference is between minus 8F and plus 8F, then the system passes the required refrigerant charge criterion.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 44

6. For the Installer, if the difference is greater than plus 5F, then the system does not pass the required refrigerant charge criterion and the Installer shall add refrigerant. Adjust refrigerant charge and check the measurements as many times as necessary to pass the test. After the final adjustment has been made, allow the system to run 15 minutes before completing the final measurement procedure. 7. For the Installer, if the difference is between minus 5F and minus 100F, then the system does not pass the required refrigerant charge criterion, the Installer shall remove refrigerant. Adjust refrigerant charge and check the measurements as many times as necessary to pass the test. After the final adjustment has been made, allow the system to run 15 minutes before completing the final measurement procedure. RA3.2.2.6.2 Variable Metering Device Calculations The Subcooling Charging Method is used for systems equipped with variable metering devices. These include Thermostatic Expansion Valves (TXV) and Electronic Expansion Valves (EXV). The amount of refrigerant is set based on the subcooling and the superheat determines whether the device is working properly. 1. Calculate Actual Subcooling as the liquid line temperature minus the condenser saturation temperature. Actual Subcooling = T condenser, sat Tliquid 2. Determine the Target Subcooling specified by the manufacturer. 3. Calculate the difference between actual subcooling and target subcooling (Actual Subcooling - Target Subcooling 4. In order to allow for inevitable differences in measurements, the Pass/Fail criteria are different for the Installer and the HERS Rater. a. For the Installer, If the difference is between minus 3F and plus 3F inclusive, then the system passes the required refrigerant charge criterion. b. For the HERS Rater inspecting the system, if the difference is between minus 6F and plus 6F inclusive and the subcooling is greater than 2F, then the system passes the required refrigerant charge criterion 5. For the Installer, if the difference is greater than plus 3F, then the system does not pass the required refrigerant charge criterion and the Installer shall remove refrigerant. Adjust refrigerant charge and check the measurements as many times as necessary to pass the test. After the final adjustment has been made, allow the system to run 15 minutes before completing the final measurement procedure. 6. For the Installer, if the difference is between minus 3F and minus 100F, then the system does not pass the required refrigerant charge criterion, the Installer shall add refrigerant. Adjust refrigerant charge and check the measurements as many times as necessary to pass the test. After the final adjustment has been made, allow the system to run 15 minutes before completing the final measurement procedure. 7. Calculate Actual Superheat as the suction line temperature minus the evaporator saturation temperature. Actual Superheat = T suction Tevaporator, sat. 8. If possible, determine the Superheat Range specified by the manufacturer. 9. In order to allow for inevitable differences in measurements, the Pass/Fail criteria are different for the Installer and the HERS Rater.

2013 California Building Energy Efficiency Standards

December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 45

a. For the Installer, if the superheat is within the manufacturers superheat range, then the system passes the metering device criterion. If the manufacturers specification is not available and the superheat is between 4F and 25F, then the system passes the metering device criterion. b. For the HERS Rater inspecting the system, if the superheat is between 3F and 26F, then the system passes the metering device criterion.

5.1.7 RA3.2.XXX Liquid Line Temperature Charging Method The Liquid Line Temperature Charging Method is used only for systems which the manufacturer specifies that charging method and provides a target liquid line temperature based on the operating conditions. An example of one manufacturers target liquid line temperature table is reproduced below. This method improves the accuracy of refrigerant charging particularly in units with low refrigerant volume in the condenser (such as microchannel heat exchangers).

Simulated Liquid Line Temperature Target Table The procedure for charging these units is: 1. Follow the manufacturers directions and adhere to their limitations on indoor and outdoor temperatures appropriate to this procedure. 2. Start the unit air conditioner and allow it to stabilize for 15 minutes. 3. Measure the liquid line temperature Tliquid, the low side pressure, Plow, and the liquid (high side) pressure Phigh. 4. Determine the minimum liquid line temperature and maximum high side pressure from the manufacturers table. 5. Determine the difference between the liquid line temperature and the minimum liquid line temperature (Actual Temperature Minimum Temperature). 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 46

6. In order to allow for inevitable differences in measurements, the Pass/Fail criteria are different for the Installer and the HERS Rater.a.

For the Installer, If the difference is between minus 0F and plus 2F (inclusive) AND the high side pressure is less than the listed maximum liquid (high side) pressure , then the system passes the required refrigerant charge criterion. For the HERS Rater inspecting the system, if the difference is between minus 2 F and plus 4F (inclusive), then the system passes the required refrigerant charge criterion

b.

7. For the Installer, if the difference is greater than plus 2F and less than the maximum high side pressure, then the system does not pass the required refrigerant charge criterion, the Installer shall add refrigerant. Adjust refrigerant charge and check the measurements as many times as necessary to pass the test. After the final adjustment has been made, allow the system to run 15 minutes before completing the final measurement procedure. 8. For the Installer, if the difference is negative, then the system does not pass the required refrigerant charge criterion and the Installer shall remove refrigerant. Adjust refrigerant charge and check the measurements as many times as necessary to pass the test. After the final adjustment has been made, allow the system to run 15 minutes before completing the final measurement procedure. 9. Calculate Actual Superheat as the suction line temperature minus the evaporator saturation temperature. Actual Superheat = Tsuction, Tevaporator, sat. 10. If possible, determine the Superheat Range specified by the manufacturer. 11. In order to allow for inevitable differences in measurements, the Pass/Fail criteria are different for the Installer and the HERS Rater.a.

For the Installer, if the superheat is within the manufacturers superheat range, then the system passes the metering device criterion. If the manufacturers specification is not available and the superheat is between 4F and 25F (inclusive), then the system passes the metering device criterion. For the HERS Rater inspecting the system, if the superheat is between 3F and 26F (inclusive), then the system passes the metering device criterion.

b.

5.1.8 RA3.2.3 Alternate Charge Measurement Procedure This section specifies the alternate charge measurement procedure. Under this procedure, the required refrigerant charge is calculated using the Weigh-In Charging Method. HVAC installers can use this alternate procedure in conjunction with installing and charging the system in as long as it is in accordance with the manufacturers specifications. Each unit charged with the Weigh-In Charging Method must be verified by a HERS Rater using one of the standard methods or confirm the self-diagnosis of a CID installed on that unit. HERS Raters shall not use this procedure Alternate Charge Measurement Procedure to verify compliance. . If a completed Addendum to CF6R-Mech-26 HERS is submitted the local jurisdiction Building Official shall allow the permit to be made final based on verification being done in the future when weather conditions are appropriate. 2013 California Building Energy Efficiency Standards December 2011

Residential Refrigerant Charge Testing and Related Issues

Page 47

Split system air conditioners come from the factory already charged with the standard charge indicated on the nameplate. The manufacturer supplies the charge proper for the application based on their standard liquid line length. It is the responsibility of the HVAC installer to ensure that the charge is correct for each air conditioner and to adjust the charge based on liquid line lengths different from the manufacturer's standard.

2013 California Building Energy Efficiency Standards

December 2011

Measure Information Template 7.3.2 Sensible EER Summary for BPM Unit

Page 61

The graphs and table below summarize the maximum Sensible EERs for BPM unit and the time delay at which that maximum occurs. The maximum Sensible EER and optimum time delay for each airflow and duct scenario are shown in bold italic.Sens. EER at unit BPM Sens. EER with Ducts BPM Sens. EER at unit BPM Sens. EER with Ducts BPM Sens. EER at unit BPM Sens. EER with Ducts BPM